Optical device and method for manufacturing same

ABSTRACT

An optical device includes: a base; a movable portion including an optical function portion; an elastic support portion supporting the movable portion so that the movable portion is movable along a first direction; a first comb electrode provided to the base and including a plurality of first comb fingers; and a second comb electrode including a plurality of second comb fingers. The elastic support portion includes a torsion bar extending along a second direction perpendicular to the first direction and a lever. The second comb electrode is provided to a portion of at least one of the movable portion and the elastic support portion, the portion being located on the optical function portion side with respect to the torsion bar. The first comb finger and the second comb finger adjacent to each other face each other in a direction in which the movable portion has higher external force resistance, of the second direction and a third direction perpendicular to the first direction and the second direction.

TECHNICAL FIELD

The present disclosure relates to an optical device configured as, forexample, a micro electro mechanical systems (MEMS) device and a methodfor manufacturing the same.

BACKGROUND ART

As an MEMS device, an optical device including a base, a movable portionwith an optical function portion, an elastic support portion connectedbetween the base and the movable portion and supporting the movableportion so that the movable portion is movable along a predetermineddirection, a first comb electrode provided in the base and including aplurality of first comb fingers, and a second comb electrode provided inthe elastic support portion and including a plurality of second combfingers alternately disposed with the plurality of first comb fingers isknown (for example, see Patent Literature 1). In such an optical device,there is a case in which the elastic support portion includes a torsionbar which is twisted and deformed when the movable portion moves along apredetermined direction.

CITATION LIST Non Patent Literature

-   Non Patent Literature 1: Thilo Sandner, Thomas Grasshoff, Harald    Schenk, and Andreas Kenda, “Out-of-plane translatory MEMS actuator    with extraordinary large stroke for optical path length modulation    in miniaturized FTIR Spectrometers”, SENSOR+TEST Conferences 2011,    Proceedings IRS2, pp. 151-156

SUMMARY OF INVENTION Technical Problem

In the optical device as described above, when the elastic supportportion is configured so that the movable portion largely moves along apredetermined direction, the movable portion tends to easily move alsoin a direction perpendicular to the predetermined direction. When themovable portion easily moves in the direction perpendicular to thepredetermined direction, a phenomenon (so-called sticking) in which thesecond comb finger contacts the adjacent first comb finger occurs. As aresult, there is concern that the movement of the movable portion in thepredetermined direction may be disturbed.

An object of the present disclosure is to provide an optical devicecapable of largely moving a movable portion along a predetermineddirection while suppressing the occurrence of sticking and a method formanufacturing the same.

Solution to Problem

An optical device of an aspect of the present disclosure includes: abase; a movable portion which includes an optical function portion; anelastic support portion which is connected between the base and themovable portion and supports the movable portion so that the movableportion is movable along a first direction; a first comb electrode whichis provided to the base and includes a plurality of first comb fingers;and a second comb electrode which is provided to at least one of themovable portion and the elastic support portion and includes a pluralityof second comb fingers arranged alternately with the plurality of firstcomb fingers, in which the elastic support portion includes a torsionbar extending along a second direction perpendicular to the firstdirection and a lever connected to the torsion bar, in which the secondcomb electrode is provided to a portion of at least one of the movableportion and the elastic support portion, the portion being located onthe optical function portion side with respect to the torsion bar, andin which the first comb finger and the second comb finger which areadjacent to each other face each other in a direction in which themovable portion has higher external force resistance, of the seconddirection and a third direction perpendicular to the first direction andthe second direction.

An optical device of an aspect of the present disclosure includes: abase; a movable portion which includes an optical function portion; anelastic support portion which is connected between the base and themovable portion and supports the movable portion so that the movableportion is movable along a first direction; a first comb electrode whichis provided to the base and includes a plurality of first comb fingers;and a second comb electrode which is provided to at least one of themovable portion and the elastic support portion and includes a pluralityof second comb fingers arranged alternately with the plurality of firstcomb fingers, in which the elastic support portion includes a torsionbar extending along a second direction perpendicular to the firstdirection and a lever connected to the torsion bar, in which the secondcomb electrode is provided to a portion of at least one of the movableportion and the elastic support portion, the portion being located onthe optical function portion side with respect to the torsion bar, andin which the first comb finger and the second comb finger which areadjacent to each other face each other in a direction in which themovable portion has the highest external force resistance, of directionsperpendicular to the first direction.

In such an optical device, the elastic support portion includes thetorsion bar and the lever and the second comb electrode is provided to aportion of at least one of the movable portion and the elastic supportportion, the portion being located on the optical function portion sidewith respect to the torsion bar. Accordingly, it is possible to largelymove the movable portion along the first direction without generating alarge electrostatic force between the first comb electrode and thesecond comb electrode. Further, the first comb finger and the secondcomb finger which are adjacent to each other face each other in thedirection in which the movable portion has higher or highest externalforce resistance. Accordingly, when the movable portion moves along thefirst direction, the second comb finger hardly contacts the adjacentfirst comb finger. As described above, according to such an opticaldevice, it is possible to largely move the movable portion along apredetermined direction (the first direction) while suppressing theoccurrence of sticking.

In the optical device of an aspect of the present disclosure, a pair ofthe elastic support portions may be disposed on both sides of themovable portion in the third direction. As compared with, for example, acase in which three or more elastic support portions are disposed aroundthe movable portion, when the pair of elastic support portions aredisposed on both sides of the movable portion, it is possible to largelymove the movable portion along the first direction with a simplerconfiguration. On the other hand, as compared with, for example, a casein which three or more elastic support portions are disposed around themovable portion, when the pair of elastic support portions are disposedon both sides of the movable portion, the movable portion tends toeasily move also in a direction perpendicular to the first direction.However, since the first comb finger and the second comb finger whichare adjacent to each other face each other in the direction in which themovable portion has high external force resistance, the occurrence ofsticking can be suppressed.

In the optical device of an aspect of the present disclosure, thedirection in which the movable portion has higher external forceresistance may be the second direction, the elastic support portion mayfurther include an electrode support member provided on the opticalfunction portion side with respect to the torsion bar so as to extendalong a plane perpendicular to the first direction, and the second combelectrode may be provided along the electrode support member.Accordingly, when the direction in which the movable portion has highexternal force resistance is the second direction, the second combelectrode can be disposed highly efficiently (that is, without taking anextra area) at an appropriate position (that is, a position in which themovable portion can be largely moved along the first direction withoutgenerating a large electrostatic force between the first comb electrodeand the second comb electrode).

In the optical device of an aspect of the present disclosure, thedirection in which the movable portion has higher external forceresistance may be the third direction and the second comb electrode maybe provided along an outer edge of the movable portion. Accordingly,when the direction in which the movable portion has high external forceresistance is the third direction, the second comb electrode can bedisposed highly efficiently (that is, without taking an extra area) atan appropriate position (that is, a position in which the movableportion can be largely moved along the first direction withoutgenerating a large electrostatic force between the first comb electrodeand the second comb electrode).

An optical device manufacturing method of an aspect of the presentdisclosure includes: a step of creating a model corresponding to theabove-described optical device and measuring a direction in which themovable portion has higher external force resistance, of the seconddirection and the third direction in the model; and a step ofmanufacturing the optical device so as to correspond to the model whenthe first comb finger and the second comb finger which are adjacent toeach other face each other in the direction in which the movable portionhas higher external force resistance in the model as a result ofmeasuring the direction in which the movable portion has higher externalforce resistance.

An optical device manufacturing method of an aspect of the presentdisclosure includes: a step of creating a model corresponding to theabove-described optical device and measuring a direction in which themovable portion has the highest external force resistance, of directionsperpendicular to the first direction in the model; and a step ofmanufacturing the optical device so as to correspond to the model whenthe first comb finger and the second comb finger which are adjacent toeach other face each other in the direction in which the movable portionhas the highest external force resistance in the model as a result ofmeasuring the direction in which the movable portion has the highestexternal force resistance.

According to the optical device manufacturing method, it is possible tohighly efficiently obtain the optical device capable of largely movingthe movable portion in the predetermined direction (the first direction)while suppressing the occurrence of sticking.

Advantageous Effects of Invention

According to the present disclosure, it is possible to provide anoptical device capable of largely moving a movable portion along apredetermined direction while suppressing the occurrence of sticking anda method for manufacturing the same.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a longitudinal sectional view of an optical module with anoptical device of an embodiment.

FIG. 2 is a longitudinal sectional view of the optical deviceillustrated in FIG. 1.

FIG. 3 is a plan view of the optical device illustrated in FIG. 2.

FIG. 4 is a graph showing a change in deformation amount of a torsionbar and a non-linear relaxation spring around a Y-axis direction withrespect to a movement amount of a movable mirror.

FIG. 5 is a graph showing a change in deformation amount of a torsionbar and a non-linear relaxation spring in an X-axis direction withrespect to the movement amount of the movable mirror.

(a) and (b) of FIG. 6 are schematic diagrams of an optical device of acomparative example.

(a) and (b) of FIG. 7 are schematic diagrams of the optical deviceillustrated in FIG. 3.

FIG. 8 is a graph showing a relationship between a movement amount ofthe movable mirror and a restoring force acting on the movable mirrorwhen there is nonlinearity or not.

FIG. 9 is a graph showing a movement amount of the movable mirror and arestoring force acting on the movable mirror of an embodiment and acomparative example.

FIG. 10 is a graph showing a relationship between a driving frequencyand a movement amount of the movable mirror when nonlinearity is small.

FIG. 11 is a graph showing a relationship between a driving frequencyand a movement amount of the movable mirror when nonlinearity is large.

FIG. 12 is a plan view of an optical device of a modified example.

DESCRIPTION OF EMBODIMENTS

Hereinafter, an embodiment of the present disclosure will be describedin detail with reference to the drawings. Furthermore, in the drawings,the same reference numerals will be given to the same or correspondingcomponents and a redundant part will be omitted.

[Configuration of Optical Module]

As illustrated in FIG. 1, an optical module 1 includes a mirror unit 2and a beam splitter unit 3. The mirror unit 2 includes an optical device10 and a fixed mirror 21. The optical device 10 includes a movablemirror (a movable portion) 11. In the optical module 1, the beamsplitter unit 3, the movable mirror 11, and the fixed mirror 21constitute an interference optical system for measurement light L0.Here, the interference optical system is a Michelson interferenceoptical system.

The optical device 10 includes a base 12, a drive unit 13, a firstoptical function portion 17, and a second optical function portion 18 inaddition to the movable mirror 11. The base 12 includes a main surface12 a. The movable mirror 11 includes a mirror surface (an opticalfunction portion) 11 a following a plane parallel to the main surface 12a. The movable mirror 11 is supported by the base 12 so as to be movablealong a Z-axis direction perpendicular to the main surface 12 a (adirection parallel to the Z axis, a first direction). The drive unit 13moves the movable mirror 11 along the Z-axis direction. The firstoptical function portion 17 is disposed at one side of the movablemirror 11 in an X-axis direction perpendicular to the Z-axis direction(a direction parallel to the X axis, a third direction) when viewed fromthe Z-axis direction. The second optical function portion 18 is disposedat the other side of the movable mirror 11 in the X-axis direction whenviewed from the Z-axis direction. The first optical function portion 17and the second optical function portion 18 are respectively lightpassage opening portions provided in the base 12 and are opened to oneside and the other side in the Z-axis direction. Furthermore, in theoptical module 1, the second optical function portion 18 is not used asthe light passage opening portion. When the optical device 10 is appliedto other apparatuses, there is a case in which at least one of the firstoptical function portion 17 and the second optical function portion 18is used as the optical function portion or both of the first opticalfunction portion 17 and the second optical function portion 18 are notused as the optical function portion.

The fixed mirror 21 includes a mirror surface 21 a following a planeparallel to the main surface 12 a. The position of the fixed mirror 21with respect to the base 12 is fixed. In the mirror unit 2, the mirrorsurface 11 a of the movable mirror 11 and the mirror surface 21 a of thefixed mirror 21 face one side in the Z-axis direction (the side of thebeam splitter unit 3).

The mirror unit 2 includes a support body 22, a sub-mount 23, and apackage 24 in addition to the optical device 10 and the fixed mirror 21.The package 24 accommodates the optical device 10, the fixed mirror 21,the support body 22, and the sub-mount 23. The package 24 includes abottom wall 241, a side wall 242, and a ceiling wall 243. The package 24is formed in, for example, a rectangular parallelepiped box shape. Thepackage 24 has, for example, a size of about 30×25×10 (thickness) mm.The bottom wall 241 and the side wall 242 are integrally formed witheach other. The ceiling wall 243 faces the bottom wall 241 in the Z-axisdirection and is fixed to the side wall 242. The ceiling wall 243 hasoptical transparency with respect to the measurement light L0. In themirror unit 2, a space S is formed by the package 24. The space S isopened to the outside of the mirror unit 2 through, for example, aventilation hole, a gap, or the like provided in the package 24. In thisway, when the space S is not an airtight space, contamination, clouding,or the like of the mirror surface 11 a caused by an out gas from theresin material present in the package 24, moisture present in thepackage 24, or the like can be suppressed. Additionally, the space S maybe an airtight space in which a high degree of vacuum is maintained oran airtight space filled with an inert gas such as nitrogen.

The support body 22 is fixed to the inner surface of the bottom wall 241through the sub-mount 23. The support body 22 is formed in, for example,a rectangular plate shape. The support body 22 has optical transparencywith respect to the measurement light L0. The base 12 of the opticaldevice 10 is fixed to a surface 22 a at the side opposite to thesub-mount 23 in the support body 22. That is, the base 12 is supportedby the support body 22. A concave portion 22 b is formed on the surface22 a of the support body 22 and a gap (a part of the space S) is formedbetween the optical device 10 and the ceiling wall 243. Accordingly, thecontact of the movable mirror 11 and the drive unit 13 with respect tothe support body 22 and the ceiling wall 243 is prevented when themovable mirror 11 is moved along the Z-axis direction.

An opening 23 a is formed in the sub-mount 23. The fixed mirror 21 isdisposed on a surface 22 c at the side of the sub-mount 23 in thesupport body 22 so as to be located within the opening 23 a. That is,the fixed mirror 21 is disposed on the surface 22 c at the side oppositeto the base 12 in the support body 22. The fixed mirror 21 is disposedat one side of the movable mirror 11 in the X-axis direction when viewedfrom the Z-axis direction. The fixed mirror 21 overlaps the firstoptical function portion 17 of the optical device 10 when viewed fromthe Z-axis direction.

The mirror unit 2 further includes a plurality of lead pins 25 and aplurality of wires 26. Each lead pin 25 is fixed to the bottom wall 241while penetrating the bottom wall 241. Each lead pin 25 is electricallyconnected to the drive unit 13 through a wire 26. In the mirror unit 2,an electric signal for moving the movable mirror 11 along the Z-axisdirection is applied to the drive unit 13 through the plurality of leadpins 25 and the plurality of wires 26.

The beam splitter unit 3 is supported by the ceiling wall 243 of thepackage 24. Specifically, the beam splitter unit 3 is fixed to a surface243 a at the side opposite to the optical device 10 in the ceiling wall243 by an optical resin 4. The optical resin 4 has optical transparencywith respect to the measurement light L0.

The beam splitter unit 3 includes a half mirror surface 31, a totalreflection mirror surface 32, and a plurality of optical surface 33 a,33 b, 33 c, and 33 d. The beam splitter unit 3 is configured by bondinga plurality of optical blocks. The half mirror surface 31 is formed by,for example, a dielectric multilayer. The total reflection mirrorsurface 32 is formed by, for example, a metal film.

The optical surface 33 a is, for example, a surface perpendicular to theZ-axis direction and overlaps the first optical function portion 17 ofthe optical device 10 and the mirror surface 21 a of the fixed mirror 21when viewed from the Z-axis direction. The measurement light L0 which isincident along the Z-axis direction is transmitted through the opticalsurface 33 a.

The half mirror surface 31 is, for example, a surface inclined by 45°with respect to the optical surface 33 a and overlaps the first opticalfunction portion 17 of the optical device 10 and the mirror surface 21 aof the fixed mirror 21 when viewed from the Z-axis direction. The halfmirror surface 31 reflects a part of the measurement light L0, which isincident to the optical surface 33 a along the Z-axis direction, alongthe X-axis direction and transmits the remaining part of the measurementlight L0 toward the fixed mirror 21 along the Z-axis direction.

The total reflection mirror surface 32 is a surface parallel to the halfmirror surface 31, overlaps the mirror surface 11 a of the movablemirror 11 when viewed from the Z-axis direction, and overlaps the halfmirror surface 31 when viewed from the X-axis direction. The totalreflection mirror surface 32 reflects a part of the measurement light L0reflected by the half mirror surface 31 toward the movable mirror 11along the Z-axis direction.

The optical surface 33 b is a surface parallel to the optical surface 33a and overlaps the mirror surface 11 a of the movable mirror 11 whenviewed from the Z-axis direction. The optical surface 33 b transmits apart of the measurement light L0 reflected by the total reflectionmirror surface 32 toward the movable mirror 11 along the Z-axisdirection.

The optical surface 33 c is a surface parallel to the optical surface 33a and overlaps the mirror surface 21 a of the fixed mirror 21 whenviewed from the Z-axis direction. The optical surface 33 c transmits theremaining part of the measurement light L0 transmitted through the halfmirror surface 31 toward the fixed mirror 21 along the Z-axis direction.

The optical surface 33 d is, for example, a surface perpendicular to theX-axis direction and overlaps the half mirror surface 31 and the totalreflection mirror surface 32 when viewed from the X-axis direction. Theoptical surface 33 d transmits the measurement light L1 along the X-axisdirection. The measurement light L1 is the interference light of a partof the measurement light L0 sequentially reflected by the mirror surface11 a of the movable mirror 11 and the total reflection mirror surface 32and transmitted through the half mirror surface 31 and the remainingpart of the measurement light L0 sequentially reflected by the mirrorsurface 21 a of the fixed mirror 21 and the half mirror surface 31.

In the optical module 1 with the above-described configuration, when themeasurement light L0 is incident from the outside of the optical module1 to the beam splitter unit 3 through the optical surface 33 a, a partof the measurement light L0 is sequentially reflected by the half mirrorsurface 31 and the total reflection mirror surface 32 and travels towardthe mirror surface 11 a of the movable mirror 11. Then, a part of themeasurement light L0 is reflected by the mirror surface 11 a of themovable mirror 11, travels in the reverse direction on the same opticalpath (an optical path P1 to be described later), and is transmittedthrough the half mirror surface 31 of the beam splitter unit 3.

Meanwhile, the remaining part of the measurement light L0 is transmittedthrough the half mirror surface 31 of the beam splitter unit 3, passesthrough the first optical function portion 17, is further transmittedthrough the support body 22, and travels toward the mirror surface 21 aof the fixed mirror 21. Then, the remaining part of the measurementlight L0 is reflected by the mirror surface 21 a of the fixed mirror 21,travels in the reverse direction on the same optical path (an opticalpath P2 to be described later), and is reflected by the half mirrorsurface 31 of the beam splitter unit 3.

Apart of the measurement light L0 transmitted through the half mirrorsurface 31 of the beam splitter unit 3 and the remaining part of themeasurement light L0 reflected by the half mirror surface 31 of the beamsplitter unit 3 become the measurement light L1 that is the interferencelight and the measurement light L1 is emitted from the beam splitterunit 3 to the outside of the optical module 1 through the opticalsurface 33 d. According to the optical module 1, since it is possible toreciprocate the movable mirror 11 at a high speed along the Z-axisdirection, a small and highly accurate Fourier transform infraredspectrometer (FTIR) can be provided.

The support body 22 corrects an optical path difference between anoptical path P1 between the beam splitter unit 3 and the movable mirror11 and an optical path P2 between the beam splitter unit 3 and the fixedmirror 21. Specifically, the optical path P1 is an optical pathextending from the half mirror surface 31 to the mirror surface 11 a ofthe movable mirror 11 located at the reference position through thetotal reflection mirror surface 32 and the optical surface 33 b in asequential order and is an optical path along which a part of themeasurement light L0 travels. The optical path P2 is an optical pathextending from the half mirror surface 31 to the mirror surface 21 a ofthe fixed mirror 21 through the optical surface 33 c and the firstoptical function portion 17 in a sequential order and is an optical pathalong which the remaining part of the measurement light L0 travels. Thesupport body 22 corrects the optical path difference between the opticalpath P1 and the optical path P2 so that a difference between the opticalpath length of the optical path P1 (the optical path length consideringthe refractive index of each medium through which the optical path P1passes) and the optical path length of the optical path P2 (the opticalpath length considering the refractive index of each medium throughwhich the optical path P2 passes) decreases. Furthermore, the supportbody 22 can be formed of, for example, a material having the sameoptical transparency as that of each of the optical blocks constitutingthe beam splitter unit 3. In this case, the thickness (the length in theZ-axis direction) of the support body 22 can be the same as the distancebetween the half mirror surface 31 and the total reflection mirrorsurface 32 in the X-axis direction.

[Configuration of Optical Device]

As illustrated in FIGS. 2 and 3, a portion other than the mirror surface11 a of the movable mirror 11, the base 12, the drive unit 13, the firstoptical function portion 17, and the second optical function portion 18are configured by a silicon on insulator (SOI) substrate 50. That is,the optical device 10 is formed by the SOI substrate 50. The opticaldevice 10 is formed in, for example, a rectangular plate shape. Theoptical device 10 has, for example, a size of about 15×10×0.3(thickness) mm. The SOI substrate 50 includes a support layer 51, adevice layer 52, and an intermediate layer 53. Specifically, the supportlayer 51 is a first silicon layer of the SOI substrate 50. The devicelayer 52 is a second silicon layer of the SOI substrate 50. Theintermediate layer 53 is an insulation layer of the SOI substrate 50 andis disposed between the support layer 51 and the device layer 52. Themovable mirror 11 and the drive unit 13 are integrally formed in a partof the device layer 52 by an MEMS technology (patterning and etching).

The base 12 is formed by the support layer 51, the device layer 52, andthe intermediate layer 53. The main surface 12 a of the base 12 is asurface at the side opposite to the intermediate layer 53 in the devicelayer 52. A main surface 12 b facing the main surface 12 a in the base12 is a surface at the side opposite to the intermediate layer 53 in thesupport layer 51. In the optical module 1, the main surface 12 a of thebase 12 is bonded to the surface 22 a of the support body 22 (see FIG.1).

The movable mirror 11 includes a main body 111, an annular portion 112,a pair of connection portions 113, and a wall portion 114. The main body111, the annular portion 112, and the pair of connection portions 113are formed by the device layer 52. The main body 111 has a circularshape when viewed from the Z-axis direction, but may have an arbitraryshape such as an octagonal shape. A metal film is formed on a surface111 a at the side of the main surface 12 b in the main body 111 so thatthe mirror surface 11 a is provided. The annular portion 112 is formedin an annular shape so as to surround the main body 111 when viewed fromthe Z-axis direction. The inner edge and the outer edge of the annularportion 112 are formed in an octagonal shape when viewed from the Z-axisdirection, but may be formed in an arbitrary shape such as a circularshape. The pair of connection portions 113 are respectively disposed atone side and the other side of the Y-axis direction perpendicular to theZ-axis direction and the X-axis direction (a direction parallel to the Yaxis, a second direction) with respect to the main body 111. Eachconnection portion 113 connects the main body 111 and the annularportion 112 to each other.

The wall portion 114 is formed by the support layer 51 and theintermediate layer 53. The wall portion 114 includes an inner wallportion 114 a, an outer wall portion 114 b, and a pair of connectionportions 114 c. The inner wall portion 114 a is provided in the surface111 a of the main body 111. The inner wall portion 114 a surrounds themirror surface 11 a when viewed from the Z-axis direction. As anexample, the inner wall portion 114 a is provided in the surface 111 aof the main body 111 so as to follow the outer edge at the inside of theouter edge of the main body 111 when viewed from the Z-axis directionand to follow the outer edge at the outside of the outer edge of themirror surface 11 a when viewed from the Z-axis direction.

The outer wall portion 114 b is provided in a surface 112 a at the sideof the main surface 12 b in the annular portion 112. As an example, theouter wall portion 114 b is provided in the surface 112 a of the annularportion 112 so as to follow the outer edge at the inside of the outeredge of the annular portion 112 when viewed from the Z-axis directionand to follow the inner edge at the outside of the inner edge of theannular portion 112 when viewed from the Z-axis direction. The pair ofconnection portions 114 c are respectively provided in a surface at theside of the main surface 12 b in the pair of connection portions 113.Each connection portion 114 c connects the inner wall portion 114 a andthe outer wall portion 114 b to each other.

The movable mirror 11 further includes a pair of brackets 116. Eachbracket 116 is formed by the device layer 52. Each bracket 116 has arectangular shape when viewed from the Z-axis direction. One bracket 116is provided in a surface at the side of the first optical functionportion 17 in the annular portion 112 so as to protrude toward the firstoptical function portion 17. The other bracket 116 is provided in asurface at the side of the second optical function portion 18 in theannular portion 112 so as to protrude toward the second optical functionportion 18 (the side opposite to the first optical function portion 17).

The drive unit 13 includes a first elastic support portion (an elasticsupport portion) 14, a second elastic support portion (an elasticsupport portion) 15, and an actuator 16. The first elastic supportportion 14, the second elastic support portion 15, and the actuator 16are formed by the device layer 52.

A pair of the first elastic support portion 14 and the second elasticsupport portion 15 are provided at both sides of the movable mirror 11in the X-axis direction. Each of the first elastic support portion 14and the second elastic support portion 15 is connected between the base12 and the movable mirror 11. The first elastic support portion 14 andthe second elastic support portion 15 support the movable mirror 11 sothat the movable mirror 11 is movable along the Z-axis direction.

The first elastic support portion 14 includes a pair of levers 141, apair of brackets 142, a link 143, a pair of electrode support members144, a pair of brackets 145, a link 146, a pair of first torsion bars(torsion bars) 147, a pair of second torsion bars 148, and a pair ofnon-linear relaxation springs 149. The pair of levers 141 extend along aplane perpendicular to the Z-axis direction from the movable mirror 11toward both sides of the first optical function portion 17 in the Y-axisdirection. In this embodiment, the pair of levers 141 extend along themain surface 12 a of the base 12 from a gap between the movable mirror11 and the first optical function portion 17 toward both sides of thefirst optical function portion 17 in the Y-axis direction.

Each lever 141 includes a first portion 141 a which is disposed at theside of the movable mirror 11 and a second portion 141 b which isdisposed at the side opposite to the movable mirror 11 with respect tothe first portion 141 a. In the pair of levers 141, the first portions141 a extend obliquely so as to be separated from each other as it goesaway from the movable mirror 11. Each second portion 141 b extends alongthe X-axis direction.

The pair of brackets 142 are provided in a surface at the side of themovable mirror 11 in the first portion 141 a so as to protrude towardthe movable mirror 11. Each bracket 142 is bent in a crank shape to thesame side when viewed from the Z-axis direction. The link 143 is laidbetween end portions 141 c at the side of the movable mirror 11 in thelevers 141. The link 143 extends along the Y-axis direction.

Each electrode support member 144 has a rectangular shape when viewedfrom the Z-axis direction. One electrode support member 144 extendsbetween one lever 141 and the movable mirror 11 and protrudes outward inrelation to the movable mirror 11 in the Y-axis direction. The otherelectrode support member 144 extends between the other lever 141 and themovable mirror 11 and protrudes outward in relation to the movablemirror 11 in the Y-axis direction. The pair of electrode support members144 are disposed on the same center line parallel to the Y-axisdirection when viewed from the Z-axis direction.

The pair of brackets 145 are provided in a surface at the side of thefirst optical function portion 17 in the electrode support member 144 soas to protrude toward the first optical function portion 17. Eachbracket 145 is bent in a crank shape to the same side (here, the sideopposite to each bracket 142) when viewed from the Z-axis direction. Thefront end portion of one bracket 145 faces the front end portion of onebracket 142 in the Y-axis direction. The front end portion of the otherbracket 145 faces the front end portion of the other bracket 142 in theY-axis direction.

The link 146 is laid between the inner end portions of the electrodesupport members 144. The link 146 is formed in a substantially U-shapewhich is opened toward the movable mirror 11 when viewed from the Z-axisdirection. The link 146 faces one bracket 116 of the movable mirror 11in the Y-axis direction. More specifically, the link 146 includes a pairof side portions 146 a extending in the X-axis direction and facing eachother in the Y-axis direction and one bracket 116 is disposed betweenthe pair of side portions 146 a.

The first torsion bar 147 is laid between the front end portion of onebracket 142 and the front end portion of one bracket 145 and between thefront end portion of the other bracket 142 and the front end portion ofthe other bracket 145. The first torsion bar 147 is laid between thebracket 142 and the bracket 145 which bent in a crank shape to theopposite side. One first torsion bar 147 is connected to the end portion141 c of one lever 141 through one bracket 142 and extends in the Y-axisdirection. The other first torsion bar 147 is connected to the endportion 141 c of the other lever 141 through the other bracket 142 andextends in the Y-axis direction. The pair of first torsion bars 147 aredisposed on the same axis parallel to the Y-axis direction.

The second torsion bar 148 is laid between the base 12 and the endportion 141 d at the side opposite to the movable mirror 11 in one lever141 and between the base 12 and the end portion 141 d at the sideopposite to the movable mirror 11 in the other lever 141. That is, theend portion 141 d of each lever 141 is connected to the base 12 throughthe second torsion bar 148. The end portion 141 d of each lever 141 isprovided with a protrusion portion 141 e protruding outward in theY-axis direction and the second torsion bar 148 is connected to theprotrusion portion 141 e. One second torsion bar 148 is connected to theend portion 141 d of one lever 141 through one protrusion portion 141 eand extends along the Y-axis direction. The other second torsion bar 148is connected to the end portion 141 d of the other lever 141 through theother protrusion portion 141 e and extends along the Y-axis direction.The pair of second torsion bars 148 are disposed on the same axisparallel to the Y-axis direction.

The pair of non-linear relaxation springs 149 are respectively disposedat one side and the other side of the Y-axis direction with respect toone bracket 116 of the movable mirror 11. Each non-linear relaxationspring 149 is connected to the movable mirror 11 through one bracket 116and is connected to the first torsion bar 147 through the link 146, theelectrode support member 144, and the bracket 145. That is, eachnon-linear relaxation spring 149 is connected between the movable mirror11 and the first torsion bar 147. Each non-linear relaxation spring 149includes a pair of plate-shaped portions 149 a laid between one bracket116 and the pair of side portions 146 a of the link 146.

Each plate-shaped portion 149 a has a flat plate shape which isperpendicular to the X-axis direction. In one non-linear relaxationspring 149, the pair of plate-shaped portions 149 a face each other inthe X-axis direction. In the pair of non-linear relaxation springs 149,the plate-shaped portion 149 a located at one side in the X-axisdirection is disposed along one plane perpendicular to the X-axisdirection and the plate-shaped portion 149 a located at the other sidein the X-axis direction is disposed along another plane perpendicular tothe X-axis direction.

Each plate-shaped portion 149 a is formed to have, for example, a length(a length in the Y-axis direction) of about 380 μm, a width (a length inthe X-axis direction) of about 5 to 10 μm, and a thickness (a length inthe Z-axis direction) of about 70 μm. The length of each plate-shapedportion 149 a is longer than each of the length of the first torsion bar147 and the length of the second torsion bar 148. The width of eachplate-shaped portion 149 a is narrower than each of the width of thefirst torsion bar 147 and the width of the second torsion bar 148.Furthermore, when at least one of the end portion at the side of thebracket 116 and the end portion at the side of the side portion 146 a inthe plate-shaped portion 149 a is provided with a wide portion which iswider as it goes away from the end portion, the length of theplate-shaped portion 149 a means the length of the plate-shaped portion149 a without the wide portion. The same applies to each of the firsttorsion bar 147 and the second torsion bar 148 and to each of a firsttorsion bar 157, a second torsion bar 158, and a plate-shaped portion159 a which will be described later.

The second elastic support portion 15 includes a pair of levers 151, apair of brackets 152, a link 153, a pair of electrode support members154, a pair of brackets 155, a link 156, a pair of first torsion bars(torsion bars) 157, a pair of second torsion bars 158, and a pair ofnon-linear relaxation springs 159. The pair of levers 151 extend along aplane perpendicular to the Z-axis direction from the movable mirror 11toward both sides of the second optical function portion 18 in theY-axis direction. In this embodiment, the pair of levers 151 extendalong the main surface 12 a of the base 12 from a gap between themovable mirror 11 and the second optical function portion 18 toward bothsides of the second optical function portion 18 in the Y-axis direction.

Each lever 151 includes a first portion 151 a which is disposed at theside of the movable mirror 11 and a second portion 151 b which isdisposed at the side opposite to the movable mirror 11 with respect tothe first portion 151 a. In the pair of levers 151, the first portions151 a extend obliquely so as to be separated from each other as it goesaway from the movable mirror 11. Each second portion 151 b extends alongthe X-axis direction.

The pair of brackets 152 are provided in a surface at the side of themovable mirror 11 in the first portion 151 a so as to protrude towardthe movable mirror 11. Each bracket 152 is bent in a crank shape to thesame side (here, the side opposite to each bracket 142) when viewed fromthe Z-axis direction. The link 153 is laid between the end portions 151c at the side of the movable mirror 11 in the levers 151. The link 153extends along the Y-axis direction.

Each electrode support member 154 has a rectangular shape when viewedfrom the Z-axis direction. One electrode support member 154 extendsbetween one lever 151 and the movable mirror 11 and protrudes outward inrelation to the movable mirror 11 in the Y-axis direction. The otherelectrode support member 154 extends between the other lever 151 and themovable mirror 11 and protrudes outward in relation to the movablemirror 11 in the Y-axis direction. The pair of electrode support members154 are disposed on the same center line parallel to the Y-axisdirection when viewed from the Z-axis direction.

The pair of brackets 155 are provided in a surface at the side of thesecond optical function portion 18 in the electrode support member 154so as to protrude toward the second optical function portion 18. Eachbracket 155 is bent in a crank shape to the same side (here, the sideopposite to each bracket 152) when viewed from the Z-axis direction. Thefront end portion of one bracket 155 faces the front end portion of onebracket 152 in the Y-axis direction. The front end portion of the otherbracket 155 faces the front end portion of the other bracket 152 in theY-axis direction.

The link 156 is laid between the inner end portions of the electrodesupport members 154. The link 156 is formed in a substantially U-shapewhich is opened toward the movable mirror 11 when viewed from the Z-axisdirection. The link 156 faces the other bracket 116 of the movablemirror 11 in the Y-axis direction. More specifically, the link 156includes a pair of side portions 156 a extending in the X-axis directionand facing each other in the Y-axis direction and the other bracket 116is disposed between the pair of side portions 156 a.

The first torsion bar 157 is laid between the front end portion of onebracket 152 and the front end portion of one bracket 155 and between thefront end portion of the other bracket 152 and the front end portion ofthe other bracket 155. The first torsion bar 157 is laid between thebracket 152 and the bracket 155 bent in a crank shape to the oppositeside. One first torsion bar 157 is connected to the end portion 151 c ofone lever 151 through one bracket 152 and extends in the Y-axisdirection. The other first torsion bar 157 is connected to the endportion 151 c of the other lever 151 through the other bracket 152 andextends in the Y-axis direction. The pair of first torsion bars 157 aredisposed on the same axis parallel to the Y-axis direction.

The second torsion bar 158 is laid between the base 12 and the endportion 151 d at the side opposite to the movable mirror 11 in one lever151 and between the base 12 and the end portion 151 d at the sideopposite to the movable mirror 11 in the other lever 151. That is, theend portion 151 d of each lever 151 is connected to the base 12 throughthe second torsion bar 158. The end portion 151 d of each lever 151 isprovided with a protrusion portion 5 e protruding outward in the Y-axisdirection and the second torsion bar 158 is connected to the protrusionportion 151 e. One second torsion bar 158 is connected to the endportion 151 d of one lever 151 through one protrusion portion 151 e andextends in the Y-axis direction. The other second torsion bar 158 isconnected to the end portion 151 d of the other lever 151 through theother protrusion portion 151 e and extends along the Y-axis direction.The pair of second torsion bars 158 are disposed on the same axisparallel to the Y-axis direction.

The pair of non-linear relaxation springs 159 are respectively disposedat one side and the other side of the Y-axis direction with respect tothe other bracket 116 of the movable mirror 11. Each non-linearrelaxation spring 159 is connected to the movable mirror 11 through theother bracket 116 and is connected to the first torsion bar 157 throughthe link 156, the electrode support member 154, and the bracket 155.That is, each non-linear relaxation spring 159 is disposed between themovable mirror 11 and the first torsion bar 157. Each non-linearrelaxation spring 159 includes a pair of plate-shaped portions 159 alaid between the other bracket 116 and the pair of side portions 156 aof the link 156.

Each plate-shaped portion 159 a has a flat plate shape which isperpendicular to the X-axis direction. In one non-linear relaxationspring 159, the pair of plate-shaped portions 159 a face each other inthe X-axis direction. In the pair of non-linear relaxation springs 159,the plate-shaped portion 159 a located at one side in the X-axisdirection is disposed along one plane perpendicular to the X-axisdirection and the plate-shaped portion 159 a located at the other sidein the X-axis direction is disposed along another plane perpendicular tothe X-axis direction.

Each plate-shaped portion 159 a is formed in, for example, the sameshape as that of the plate-shaped portion 149 a. The length of eachplate-shaped portion 159 a is longer than each of the length of thefirst torsion bar 157 and the length of the second torsion bar 158. Thewidth of each plate-shaped portion 159 a is narrower than the width ofthe first torsion bar 157 and the width of the second torsion bar 158.

Each of the first optical function portion 17 and the second opticalfunction portion 18 is a light passage opening portion formed in the SOIsubstrate 50. Each of the first optical function portion 17 and thesecond optical function portion 18 has a circular cross-sectional shapewhen viewed from the Z-axis direction, but may be formed in an arbitraryshape such as an octagonal cross-sectional shape. The first opticalfunction portion 17 and the second optical function portion 18 may bevoid and may be formed of a material having optical transparency withrespect to the measurement light L0.

The first elastic support portion 14 and the second elastic supportportion 15 do not have a symmetrical structure with respect to a planepassing through the center of the movable mirror 11 and perpendicular tothe X-axis direction and a plane passing through the center of themovable mirror 11 and perpendicular to the Y-axis direction. Here, aportion excluding the pair of brackets 142 and the pair of brackets 145in the first elastic support portion 14 and a portion excluding the pairof brackets 152 and the pair of brackets 155 in the second elasticsupport portion 15 have a symmetrical structure with respect to a planepassing through the center of the movable mirror 11 and perpendicular tothe X-axis direction and a plane passing through the center of themovable mirror 11 and perpendicular to the Y-axis direction.

The actuator 16 moves the movable mirror 11 along the Z-axis direction.The actuator 16 includes a pair of first comb electrodes 161, a pair ofsecond comb electrodes 162, a pair of first comb electrodes 163, and apair of second comb electrodes 164. The first comb electrodes 161 and163 are fixed comb electrodes of which positions are fixed and thesecond comb electrodes 162 and 164 are movable comb electrodes whichmove in accordance with the movement of the movable mirror 11.

The pair of first comb electrodes 161 are provided in the base 12.Specifically, one first comb electrode 161 is provided in a surfacefacing one electrode support member 144 in the device layer 52 of thebase 12. The other first comb electrode 161 is provided in a surfacefacing the other electrode support member 144 in the device layer 52.Each first comb electrode 161 includes a plurality of first comb fingers161 a extending along a plane perpendicular to the Y-axis direction. Thefirst comb fingers 161 a are arranged side by side with a predeterminedinterval in the Y-axis direction.

The pair of second comb electrodes 162 are provided at a portion locatedat the side of the mirror surface 11 a in the X-axis direction inrelation to the pair of first torsion bars 147 of the first elasticsupport portion 14. Specifically, one second comb electrode 162 isprovided in each of a surface at the side of the movable mirror 11 and asurface at the side of the lever 141 in one electrode support member144. The other second comb electrode 162 is provided in each of asurface at the side of the movable mirror 11 and a surface at the sideof the lever 141 in the other electrode support member 144. Each secondcomb electrode 162 includes a portion located between the movable mirror11 and the lever 141 when viewed from the Z-axis direction. Each secondcomb electrode 162 includes a plurality of second comb fingers 162 aextending along a plane perpendicular to the Y-axis direction. Thesecond comb fingers 162 a are arranged side by side with a predeterminedinterval in the Y-axis direction.

In one first comb electrode 161 and one second comb electrode 162, theplurality of first comb fingers 161 a and the plurality of second combfingers 162 a are alternately arranged. That is, each first comb finger161 a of one first comb electrode 161 is located between the respectivesecond comb fingers 162 a of one second comb electrode 162. In the otherfirst comb electrode 161 and the other second comb electrode 162, theplurality of first comb fingers 161 a and the plurality of second combfingers 162 a are alternately arranged. That is, each first comb finger161 a of the other first comb electrode 161 is located between therespective second comb fingers 162 a of the other second comb electrode162. In the pair of first comb electrodes 161 and the pair of secondcomb electrodes 162, the first comb finger 161 a and the second combfinger 162 a which are adjacent to each other face each other in theY-axis direction. A distance between the first comb finger 161 a and thesecond comb finger 162 a which are adjacent to each other is, forexample, about several μm.

The pair of first comb electrodes 163 are provided in the base 12.Specifically, one first comb electrode 163 is provided in a surfacefacing one electrode support member 154 in the device layer 52 of thebase 12. The other first comb electrode 163 is provided in a surfacefacing the other electrode support member 154 in the device layer 52.Each first comb electrode 163 includes a plurality of first comb fingers163 a extending along a plane perpendicular to the Y-axis direction. Thefirst comb fingers 163 a are arranged side by side with a predeterminedinterval in the Y-axis direction.

The pair of second comb electrodes 164 are provided in a portion locatedat the side of the mirror surface 11 a in the X-axis direction inrelation to the pair of first torsion bars 157 of the second elasticsupport portion 15. Specifically, one second comb electrode 164 isprovided in each of a surface at the side of the movable mirror 11 and asurface at the side of the lever 151 in one electrode support member154. The other second comb electrode 164 is provided in each of asurface at the side of the movable mirror 11 and a surface at the sideof the lever 151 in the other electrode support member 154. Each secondcomb electrode 164 includes a portion located between the movable mirror11 and the lever 151 when viewed from the Z-axis direction. Each secondcomb electrode 164 includes a plurality of second comb fingers 164 aextending along a plane perpendicular to the Y-axis direction. Thesecond comb fingers 164 a are arranged side by side with a predeterminedinterval in the Y-axis direction.

In one first comb electrode 163 and one second comb electrode 164, theplurality of first comb fingers 163 a and the plurality of second combfingers 164 a are alternately arranged. That is, each first comb finger163 a of one first comb electrode 163 is located between the respectivesecond comb fingers 164 a of one second comb electrode 164. In the otherfirst comb electrode 163 and the other second comb electrode 164, theplurality of first comb fingers 163 a and the plurality of second combfingers 164 a are alternately arranged. That is, each first comb finger163 a of the other first comb electrode 163 is located between therespective second comb fingers 164 a of the other second comb electrode164. In the pair of first comb electrodes 163 and the pair of secondcomb electrodes 164, the first comb finger 163 a and the second combfinger 164 a which are adjacent to each other face each other in theY-axis direction. A distance between the first comb finger 163 a and thesecond comb finger 164 a which are adjacent to each other is, forexample, about several μm.

The base 12 is provided with a plurality of electrode pads 121 and 122.Each of the electrode pads 121 and 122 is formed in a surface of thedevice layer 52 inside an opening 12 c formed in the main surface 12 bof the base 12 so as to reach the device layer 52. Each electrode pad121 is electrically connected to the first comb electrode 161 or thefirst comb electrode 163 through the device layer 52. Each electrode pad122 is electrically connected to the second comb electrode 162 or thesecond comb electrode 164 through the first elastic support portion 14and the main body 111 of the movable mirror 11 or the second elasticsupport portion 15 and the main body 111 of the movable mirror 11. Thewire 26 is laid between each of the electrode pads 121 and 122 and eachlead pin 25.

In the optical device 10 with the above-described configuration, when avoltage is applied across the plurality of electrode pads 121 and theplurality of electrode pads 122 through the plurality of lead pins 25and the plurality of wires 26, an electrostatic force is generatedbetween the first comb electrodes 161 and 163 and the second combelectrodes 162 and 164 facing each other so as to move, for example, themovable mirror 11 toward one side in the Z-axis direction. At this time,in the first elastic support portion 14 and the second elastic supportportion 15, the torsion bars 147, 148, 157, and 158 are twisted so thatan elastic force is generated in the first elastic support portion 14and the second elastic support portion 15. In the optical device 10,when a periodic electric signal is applied to the drive unit 13 throughthe plurality of lead pins 25 and the plurality of wires 26, the movablemirror 11 can be reciprocated along the Z-axis direction at the resonantfrequency level. In this way, the drive unit 13 functions as anelectrostatic actuator.

[Relationship Between Torsion Bar and Non-Linear Relaxation Spring]

FIG. 4 is a graph showing a change in the deformation amount of thefirst torsion bar 147, the second torsion bar 148, and the non-linearrelaxation spring 149 around the Y-axis direction with respect to themovement amount of the movable mirror 11 in the Z-axis direction. FIG. 5is a graph showing a change in the deformation amount of the firsttorsion bar 147, the second torsion bar 148, and the non-linearrelaxation spring 149 in the X-axis direction with respect to themovement amount of the movable mirror 11 in the Z-axis direction.Furthermore, the deformation amount of the first torsion bar 147, thesecond torsion bar 148, and the non-linear relaxation spring 149 aroundthe Y-axis direction means, for example, an absolute value of a twistamount (twist angle). The deformation amount of the first torsion bar147, the second torsion bar 148, and the non-linear relaxation spring149 in the X-axis direction means, for example, an absolute value ofbending. The deformation amount of the non-linear relaxation spring 149around the Y-axis direction means, for example, the deformation amountof one plate-shaped portion 149 a constituting the non-linear relaxationspring 149 around the Y-axis direction. The deformation amount of thenon-linear relaxation spring 149 in the X-axis direction means, forexample, the deformation amount of one plate-shaped portion 149 aconstituting the non-linear relaxation spring 149 in the X-axisdirection. The deformation amount of a certain member around the Y-axisdirection means the deformation amount of the member in thecircumferential direction of the circle about the axis parallel to the Yaxis and passing through the center of the member.

As shown in FIG. 4, when the movable mirror 11 moves in the Z-axisdirection, each of the first torsion bar 147, the second torsion bar148, and the non-linear relaxation spring 149 is deformed in the samedirection around the Y-axis direction. When the movement amount of themovable mirror 11 increases, the deformation amount of each of the firsttorsion bar 147, the second torsion bar 148, and the non-linearrelaxation spring 149 around the Y-axis direction linearly increases.Comparing the deformation amount of respective members around the Y-axisdirection, when the movement amount of the movable mirror 11 is thesame, the deformation amount of the first torsion bar 147 is smallerthan the deformation amount of the second torsion bar 148 and thedeformation amount of the non-linear relaxation spring 149 is muchsmaller than each of the deformation amount of the first torsion bar 147and the deformation amount of the second torsion bar 148.

As shown in FIG. 5, when the movable mirror 11 moves in the Z-axisdirection, the non-linear relaxation spring 149 is largely deformed inthe X-axis direction and the first torsion bar 147 and the secondtorsion bar 148 are not substantially deformed in the X-axis direction.The deformation direction of the first torsion bar 147 is the same asthe deformation direction of the non-linear relaxation spring 149 and isopposite to the deformation direction of the second torsion bar 148.When the movement amount of the movable mirror 11 increases, thedeformation amount of the non-linear relaxation spring 149 in the X-axisdirection increases quadratically. Comparing the deformation amount inthe X-axis direction of respective members, when the movement amount ofthe movable mirror 11 is the same, the deformation amount of the firsttorsion bar 147 is substantially the same as the deformation amount ofthe second torsion bar 148 and the deformation amount of the non-linearrelaxation spring 149 is much larger than each of the deformation amountof the first torsion bar 147 and the deformation amount of the secondtorsion bar 148.

In this way, the non-linear relaxation spring 149 is configured so thatthe deformation amount of the non-linear relaxation spring 149 aroundthe Y-axis direction is smaller than the deformation amount of each ofthe torsion bars 147 and 148 around the Y-axis direction and thedeformation amount of the non-linear relaxation spring 149 in the X-axisdirection is larger than the deformation amount of each of the torsionbars 147 and 148 in the X-axis direction while the movable mirror 11moves in the Z-axis direction. Similarly, the non-linear relaxationspring 159 is configured so that the deformation amount of thenon-linear relaxation spring 159 around the Y-axis direction is smallerthan the deformation amount of each of the torsion bars 157 and 158around the Y-axis direction and the deformation amount of the non-linearrelaxation spring 159 in the X-axis direction is larger than thedeformation amount of each of the torsion bars 157 and 158 in the X-axisdirection while the movable mirror 11 moves in the Z-axis direction.Furthermore, a relationship between the deformation amount around theY-axis direction and the deformation amount in the X-axis direction ofthese members may be satisfied within a predetermined movable range ofthe movable mirror 11.

FIG. 6 is a schematic diagram of an optical device of a comparativeexample and FIG. 7 is a schematic diagram of the optical device 10 ofthe above-described embodiment. FIGS. 6 and 7 illustrate that a part ofthe configuration of the optical device 10 when viewed from the Y-axisdirection is simplified. The comparative example corresponds to anexample in which the non-linear relaxation springs 149 and 159 are notprovided in the optical device 10 of the above-described embodiment andeach bracket 116 is connected to the electrode support members 144 and154 by a rigid member. A movable mirror 1011, levers 1141 and 1151,first torsion bars 1147 and 1157, and second torsion bars 1148 and 1158of the comparative example respectively correspond to the movable mirror11, the levers 141 and 151, the first torsion bars 147 and 157, and thesecond torsion bars 148 and 158 of the optical device 10 of theabove-described embodiment.

Hereinafter, the side of the first torsion bar 1157 is exemplified, butthe same applies to the side of the first torsion bar 1147. Asillustrated in FIG. 6, assuming that the first torsion bar 1157 movesonly by the torsional deformation of the second torsion bar 1158 whenthe movable mirror 1011 of the comparative example moves in the Z-axisdirection, the first torsion bar 1157 moves to the position B and movesaway from the movable mirror 1011 by the distance L between the positionA and the position B. For that reason, the first torsion bar 1157 andthe second torsion bar 1158 are actually bent and deformed in the X-axisdirection by the distance L. That is, in the comparative example, whenthe movable mirror 1011 moves in the Z-axis direction, the first torsionbar 1157 and the second torsion bar 1158 are twisted in a bent state.For this reason, nonlinearity occurs in torsional deformation of thefirst torsion bar 1157 and the second torsion bar 1158. When suchnonlinearity exists, there is concern that the control characteristic ofthe movable mirror 11 may be deteriorated as will be described later.

In contrast, as illustrated in FIG. 7, when the movable mirror 11 in theoptical device 10 moves in the Z-axis direction, the non-linearrelaxation spring 159 is deformed in the X-axis direction so as to belarger than the first torsion bar 157 and the second torsion bar 158while being deformed around the Y-axis direction so as to be smallerthan the first torsion bar 157 and the second torsion bar 158.Accordingly, it is possible to suppress the first torsion bar 157 andthe second torsion bar 158 from being bent and deformed in the X-axisdirection. As a result, it is possible to suppress nonlinearity in thetorsional deformation of the first torsion bar 157 and the secondtorsion bar 158.

Here, a problem that occurs when nonlinearity exists in the torsionaldeformation of the first torsion bars 147 and 157 and the second torsionbars 148 and 158 will be described with reference to FIGS. 8 to 11. InFIG. 8, a relationship between the restoring force acting on the movablemirror 11 and the movement amount of the movable mirror 11 when there isno nonlinearity is indicated by a dashed line and the relationship whenthere is nonlinearity is indicated by a solid line. As shown in FIGS. 8and 9, if the movement amount of the movable mirror 11 in the Z-axisdirection increases when nonlinearity does not exist (decreases) as inthe optical device 10, the restoring force acting on the movable mirror11 linearly increases. Meanwhile, if the movement amount of the movablemirror 11 in the Z-axis direction increases when there is nonlinearityas in the comparative example, the restoring force acting on the movablemirror 11 increases at an accelerated rate so as to be larger than thatof the optical device 10. A spring having characteristics as in thecomparative example is called a hardened spring (or gradually hardenedspring).

FIGS. 10 and 11 are graphs showing a relationship between the drivingfrequency and the movement amount of the movable mirror 11 whennonlinearity is small and large. In FIGS. 10 and 11, a frequencycharacteristic when there is no nonlinearity is indicated by a dashedline and a frequency characteristic when there is nonlinearity isindicated by a solid line. As shown in FIGS. 10 and 11, when there isnonlinearity, the frequency characteristic is distorted and the movementamount of the movable mirror 11 at the peak of the graph is small ascompared with a case in which there is no nonlinearity. For that reason,a large force is necessary when there is nonlinearity in order to movethe movable mirror 11 by the same movement amount and hence the controlcharacteristic of the movable mirror 11 is deteriorated. Furthermore,FIGS. 10 and 11 show an example of the frequency characteristic, but thefrequency characteristic is not limited thereto.

Further, as shown in FIG. 11, when the nonlinearity increases, there maybe two solutions (multiple solutions) of the point X1 and the point X2for the same driving frequency. In this case, the behavior of themovable mirror 11 is different for the case of performing a control ofincreasing the driving frequency from a relatively small initial valueand the case of performing a control of decreasing the driving frequencyfrom a relatively large initial value. Further, when a continuousoperation is performed in a frequency range including a frequencycorresponding to multiple solutions, the movement amount of the movablemirror 11 becomes a movement amount corresponding to the point X1 orcorresponding to the point X2 due to external influences such as impactand vibration and hence the operation becomes unstable due to themovement amount. For that reason, since the control is complex, there isconcern that the control characteristic of the movable mirror 11 may bedeteriorated. Further, when there is nonlinearity, a third harmonic (afrequency component three times the target frequency) is added to theoperation waveform when the operation waveform of the movable mirror 11is controlled, for example, in a sine wave shape and hence the operationwaveform cannot be controlled in a desired shape. Accordingly, there isconcern that the control characteristic of the movable mirror 11 mayalso be deteriorated. In this way, when there is nonlinearity in thetorsional deformation of the first torsion bars 147 and 157 and thesecond torsion bars 148 and 158, there is concern that the controlcharacteristic of the movable mirror 11 may be deteriorated. Incontrast, as described above, according to the optical device 10, it ispossible to suppress the occurrence of nonlinearity and to suppressdeterioration in the control characteristic of the movable mirror 11.

[Relationship Between External Force Resistance of Movable Portion andEach of First and Second Comb Teeth]

Referring to FIG. 3, a relationship between the external forceresistance of the movable mirror 11 and each of the first comb fingers161 a and 163 a and the second comb fingers 162 a and 164 a will bedescribed. In the above-described optical device 10, the external forceresistance of the movable mirror 11 in the Y-axis direction is higherthan the external force resistance of the movable mirror 11 in theX-axis direction. The first comb finger 161 a and the second comb finger162 a which are adjacent to each other face each other in the direction(the Y-axis direction) in which the movable mirror 11 has higherexternal force resistance in the X-axis direction or the Y-axisdirection. Similarly, the first comb finger 163 a and the second combfinger 164 a which are adjacent to each other face each other in thedirection (the Y-axis direction) in which the movable mirror 11 hashigher external force resistance in the X-axis direction or the Y-axisdirection. Here, each of the first comb fingers 161 a and 163 a and thesecond comb fingers 162 a and 164 a extends along a plane perpendicularto the direction (the Y-axis direction) in which the movable mirror 11has higher external force resistance in the X-axis direction or theY-axis direction. In the above-described optical device 10, the pair ofsecond comb electrodes 162 are provided along the pair of electrodesupport members 144 extending along a plane perpendicular to the Z-axisdirection on the mirror surface 11 a side with respect to the pair offirst torsion bars 147 and the pair of second comb electrodes 164 areprovided along the pair of electrode support members 154 extending alonga plane perpendicular to the Z-axis direction on the mirror surface 11 aside with respect to the pair of first torsion bars 157.

Here, the external force resistance of the movable mirror 11 correspondsto the movement amount of the movable mirror 11 along an external forceapplying direction when an external force of a certain magnitude (forexample, acceleration) is applied to the movable mirror 11 along adirection perpendicular to the Z-axis direction and is a characteristicthat the external force resistance is higher as the movement amount issmaller. In other words, the external force resistance of the movablemirror 11 corresponds to the magnitude of the external force necessaryfor moving the movable mirror 11 by a predetermined movement amountalong a direction perpendicular to the Z-axis direction and is acharacteristic that the external force resistance is higher as themagnitude of the external force is larger.

The external force resistance of the movable mirror 11 can be obtainedfrom the natural frequency of the movable mirror 11 in a directionperpendicular to the Z-axis direction and the external force resistanceis higher as the natural frequency is higher. As an example, in theabove-described optical device 10, the natural frequency of the movablemirror 11 in the X-axis direction is about 2600 Hz and the naturalfrequency of the movable mirror 11 in the Y-axis direction is about 4300Hz. Accordingly, it is proved that the external force resistance of themovable mirror 11 in the Y-axis direction is higher than the externalforce resistance of the movable mirror 11 in the X-axis direction. Forreference, in the above-described optical device 10, the naturalfrequency of the movable mirror 11 in the Z-axis direction is about 300Hz. Furthermore, the natural frequency of the movable mirror 11 in theX-axis direction is an analysis result when the width of theplate-shaped portion 149 a (the length in the X-axis direction) is 10μm. When the width of the plate-shaped portion 149 a is 5 μm, thenatural frequency of the movable mirror 11 in the X-axis direction isabout 1100 Hz, but the natural frequency of the movable mirror 11 in theY-axis direction and the natural frequency of the movable mirror 11 inthe Z-axis direction hardly change.

[Optical Device Manufacturing Method]

A method for manufacturing the above-described optical device 10 will bedescribed. First, a model corresponding to the optical device 10 iscreated and a direction in which the movable mirror 11 has higherexternal force resistance in the Y-axis direction or the X-axisdirection in the created model is measured (a measuring step).Specifically, a simulation model is created by using a computer, anoperation analysis is performed by using the simulation model, and adirection in which the movable mirror 11 has higher external forceresistance is measured. Alternatively, an optical device is actuallymade as a model, an operation analysis is performed by using the opticaldevice, and a direction in which the movable mirror 11 has higherexternal force resistance is measured. Next, the optical device 10 ismanufactured so as to correspond to the created model when the firstcomb finger 161 a and the second comb finger 162 a which are adjacent toeach other face each other in the direction in which the movable mirror11 has higher external force resistance and the first comb finger 163 aand the second comb finger 164 a which are adjacent to each other faceeach other in the direction in which the movable mirror 11 has higherexternal force resistance in the created model as a result of measuringthe direction in which the movable mirror 11 has higher external forceresistance (a manufacturing step).

Operation and Effect

An operation and an effect of the optical device 10 and itsmanufacturing method will be described. In the optical device 10, thefirst elastic support portion 14 includes the first torsion bar 147 andthe lever 141 and the second comb electrode 162 is provided in a portion(specifically, the electrode support member 144) of the first elasticsupport portion 14, the portion being located on the mirror surface 11 aside with respect to the first torsion bar 147. Similarly, the secondelastic support portion 15 includes the first torsion bar 157 and thelever 151 and the second comb electrode 164 is provided in a portion(specifically, the electrode support member 154) of the second elasticsupport portion 15 located on the mirror surface 11 a side with respectto the first torsion bar 157. Accordingly, it is possible to largelymove the movable mirror 11 along the Z-axis direction while suppressingthe electrostatic force generated between the first comb electrode 161and the second comb electrode 162 and the electrostatic force generatedbetween the first comb electrode 163 and the second comb electrode 164.Further, the first comb finger 161 a and the second comb finger 162 awhich are adjacent to each other face each other in the Y-axis directionin which the movable mirror 11 has higher external force resistance inthe X-axis direction or the Y-axis direction. Similarly, the first combfinger 163 a and the second comb finger 164 a which are adjacent to eachother face each other in the Y-axis direction in which the movablemirror 11 has higher external force resistance in the X-axis directionor the Y-axis direction. Accordingly, when the movable mirror 11 movesin the Z-axis direction, the second comb finger 162 a hardly contactsthe first comb finger 161 a which is adjacent thereto and the secondcomb finger 164 a hardly contacts the first comb finger 163 a which isadjacent thereto. As described above, according to the optical device10, it is possible to largely move the movable mirror 11 along apredetermined direction (the Z-axis direction) while suppressing theoccurrence of sticking.

In the optical device 10, the pair of first elastic support portion 14and the second elastic support portion 15 are disposed on both sides ofthe movable mirror 11 in the X-axis direction. As compared with, forexample, a case in which three or more elastic support portions aredisposed around the movable mirror 11, when the pair of first elasticsupport portion 14 and the second elastic support portion 15 aredisposed on both sides of the movable mirror 11, it is possible tolargely move the movable mirror 11 along the Z-axis direction with asimpler configuration. On the other hand, as compared with, for example,a case in which three or more elastic support portions are disposedaround the movable mirror 11, when the pair of first elastic supportportion 14 and the second elastic support portion 15 are disposed onboth sides of the movable mirror 11, the movable mirror 11 tends toeasily move also in a direction perpendicular to the Z-axis direction.However, the first comb finger 161 a and the second comb finger 162 awhich are adjacent to each other face each other in the direction inwhich the movable mirror 11 has higher external force resistance and thefirst comb finger 163 a and the second comb finger 164 a which areadjacent to each other face each other in the direction in which themovable mirror 11 has higher external force resistance. For that reason,the occurrence of sticking can be suppressed.

In particular, when the first elastic support portion 14 is providedwith the non-linear relaxation spring 149 and the second elastic supportportion 15 is provided with the non-linear relaxation spring 159,nonlinearity is reduced as described above, but the movable mirror 11tends to easily move also in a direction perpendicular to the Z-axisdirection. For that reason, it is very effective that the first combfinger 161 a and the second comb finger 162 a which are adjacent to eachother face each other in the direction in which the movable mirror 11has higher external force resistance in the X-axis direction or theY-axis direction and the first comb finger 163 a and the second combfinger 164 a which are adjacent to each other face each other in thedirection in which the movable mirror 11 has higher external forceresistance in the X-axis direction or the Y-axis direction.

In the optical device 10, the first elastic support portion 14 includesan electrode support member 144 provided on the mirror surface 11 a sidewith respect to the first torsion bar 147 so as to extend along a planeperpendicular to the Z-axis direction and the second comb electrode 162is provided along the electrode support member 144. Similarly, thesecond elastic support portion 15 includes an electrode support member154 provided on the mirror surface 11 a side with respect to the firsttorsion bar 157 so as to extend along a plane perpendicular to theZ-axis direction and the second comb electrode 164 is provided along theelectrode support member 154. Accordingly, in the optical device 10 inwhich a direction in which the movable mirror 11 has higher externalforce resistance is the Y-axis direction, the second comb electrodes 162and 164 can be disposed efficiently (that is, without taking an extraarea) at an appropriate position (that is, a position in which themovable mirror 11 can be largely moved along the Z-axis directionwithout generating a large electrostatic force between the first combelectrode 161 and the second comb electrode 162 and between the firstcomb electrode 163 and the second comb electrode 164).

According to the method for manufacturing the optical device 10, it ispossible to highly efficiently obtain the optical device 10 capable oflargely moving the movable mirror 11 along a predetermined direction(the Z-axis direction) while suppressing the occurrence of sticking.

Modified Example

As described above, an embodiment of the present disclosure has beendescribed, but the present disclosure is not limited to theabove-described embodiment. For example, the materials and shapes ofeach component are not limited to the materials and shapes describedabove and various materials and shapes can be employed.

FIG. 12 is a plan view of the optical device 10 of a modified example.As illustrated in FIG. 12, the optical device 10 of the modified exampleis mainly different from the optical device 10 of the above-describedembodiment in that the first elastic support portion 14 and the secondelastic support portion 15 do not respectively include the pair ofelectrode support members 144 and the pair of electrode support members154 and the pair of first comb electrodes 161 and the pair of secondcomb electrodes 162 are disposed along the outer edge of the movablemirror 11.

In the optical device 10 of the modified example, the pair of first combelectrodes 161 are provided in the base 12. Specifically, the pair offirst comb electrodes 161 are respectively provided in the surfacesfacing the outer surfaces 112 a and 112 a of the annular portion 112 inthe Y-axis direction in the device layer 52 of the base 12. Each firstcomb electrode 161 includes a plurality of first comb fingers 161 aextending along a plane perpendicular to the X-axis direction. The firstcomb fingers 161 a are arranged side by side with a predeterminedinterval in the X-axis direction.

In the optical device 10 of the modified example, the pair of secondcomb electrodes 162 are provided along the outer edge of the movablemirror 11. Specifically, the pair of second comb electrodes 162 arerespectively provided in the outer surfaces 112 a and 112 a of theannular portion 112 in the Y-axis direction. In this example, the secondcomb electrodes 162 are arranged in the entire surface 112 a of theannular portion 112 when viewed from the Z-axis direction. Each secondcomb electrode 162 includes a plurality of second comb fingers 162 aextending along a plane perpendicular to the X-axis direction. Thesecond comb fingers 162 a are arranged side by side with a predeterminedinterval in the X-axis direction.

In one first comb electrode 161 and one second comb electrode 162, theplurality of first comb fingers 161 a and the plurality of second combfingers 162 a are alternately arranged. That is, each first comb finger161 a of one first comb electrode 161 is located between the respectivesecond comb fingers 162 a of one second comb electrode 162. In the otherfirst comb electrode 161 and the other second comb electrode 162, theplurality of first comb fingers 161 a and the plurality of second combfingers 162 a are alternately arranged. That is, each first comb finger161 a of the other first comb electrode 161 is located between therespective second comb fingers 162 a of the other second comb electrode162. A distance between the first comb finger 161 a and the second combfinger 162 a which are adjacent to each other is, for example, aboutseveral μm.

In the optical device 10 of the modified example, the external forceresistance of the movable mirror 11 in the X-axis direction is higherthan the external force resistance of the movable mirror 11 in theY-axis direction. The first comb finger 161 a and the second comb finger162 a which are adjacent to each other face each other in the directionin which the movable mirror 11 has higher external force resistance (theX-axis direction) in the X-axis direction or the Y-axis direction. Here,the first comb fingers 161 a and the second comb fingers 162 a extendalong a plane perpendicular to a direction in which the movable mirror11 has higher external force resistance (the X-axis direction) in theX-axis direction or the Y-axis direction.

As an example, in the optical device 10 of the modified example, thenatural frequency of the movable mirror 11 in the Y-axis direction isabout 4300 Hz and the natural frequency of the movable mirror 11 in theX-axis direction is about 4900 Hz. Accordingly, it is proved that theexternal force resistance of the movable mirror 11 in the X-axisdirection is higher than the external force resistance of the movablemirror 11 in the Y-axis direction. For reference, in the optical device10 of the modified example, the natural frequency of the movable mirror11 in the Z-axis direction is about 300 Hz.

As described above, in the optical device 10 of the modified example, adirection in which the movable mirror 11 has higher external forceresistance is the X-axis direction and the second comb electrode 162 isprovided along the outer edge of the movable mirror 11. Accordingly, inthe optical device 10 in which a direction in which the movable mirror11 has higher external force resistance is the X-axis direction, thesecond comb electrode 162 can be disposed efficiently (that is, withouttaking an extra area) at an appropriate position (that is, a position inwhich the movable mirror 11 can be largely moved along the Z-axisdirection without generating a large electrostatic force between thefirst comb electrode 161 and the second comb electrode 162).

Further, in the optical device 10 of the above-described embodiment, thefirst comb finger 161 a and the second comb finger 162 a which areadjacent to each other may face each other in the direction in which themovable mirror 11 has the highest external force resistance, ofdirection perpendiculars to the Z-axis direction. Similarly, the firstcomb finger 163 a and the second comb finger 164 a which are adjacent toeach other may face each other in the direction in which the movablemirror 11 has the highest external force resistance, of directionsperpendicular to the Z-axis direction. Such an optical device 10 can bemanufactured as below. First, a model corresponding to the opticaldevice 10 is created and a direction in which the movable mirror 11 hasthe highest external force resistance, of directions perpendicular tothe Z-axis direction in the created model is measured. Next, the opticaldevice 10 is manufactured so as to correspond to the created model whenthe first comb finger 161 a and the second comb finger 162 a which areadjacent to each other face each other in the direction in which themovable mirror 11 has the highest external force resistance and thefirst comb finger 163 a and the second comb finger 164 a which areadjacent to each other face each other in the direction in which themovable mirror 11 has the highest external force resistance in thecreated model as a result of measuring the direction in which themovable mirror 11 has the highest external force resistance.

Similarly, in the optical device 10 of the modified example, the firstcomb finger 161 a and the second comb finger 162 a which are adjacent toeach other may face each other in the direction in which the movablemirror 11 has the highest external force resistance, of directionsperpendicular to the Z-axis direction. Such an optical device 10 can bemanufactured as below. First, a model corresponding to the opticaldevice 10 is created and a direction in which the movable mirror 11 hasthe highest external force resistance, of directions perpendicular tothe Z-axis direction in the created model is measured. Next, the opticaldevice 10 is manufactured so as to correspond to the created model whenthe first comb finger 161 a and the second comb finger 162 a which areadjacent to each other face each other in the direction in which themovable mirror 11 has the highest external force resistance in thecreated model as a result of measuring the direction in which themovable mirror 11 has the highest external force resistance.

Further, the second comb electrode 162 may be provided in a portionlocated at the side of the mirror surface 11 a in relation to the firsttorsion bar 147 in the X-axis direction in at least one of the movablemirror 11 and the first elastic support portion 14. Similarly, thesecond comb electrode 164 may be provided in a portion located at theside of the mirror surface 11 a in relation to the first torsion bar 157in the X-axis direction in at least one of the movable mirror 11 and thesecond elastic support portion 15. Further, the drive unit 13 mayinclude three or more elastic support portions. The optical device 10may include a movable portion provided with another optical functionportion other than the mirror surface 11 a instead of the movable mirror11. As another optical function portion, for example, a lens or the likecan be exemplified.

Further, the first elastic support portion 14 may further include a pairof levers. As an example, the pair of levers are disposed on both sidesof the first optical function portion 17 and extend along the X-axisdirection. An end portion at the side opposite to the mirror surface 11a in one lever is connected to the protrusion portion 141 e of one lever141 through one second torsion bar 148. An end portion at the sideopposite to the mirror surface 11 a in the other lever is connected tothe protrusion portion 141 e of the other lever 141 through the othersecond torsion bar 148. An end portion at the side of the mirror surface11 a in each of the pair of levers may be fixed to the base 12 or may beconnected to the base 12 through the torsion bar. When an end portion atthe side of the mirror surface 11 a in each of the pair of levers isfixed to the base 12, for example, the pair of levers are bent anddeformed. The same applies to the second elastic support portion 15.

The non-linear relaxation spring 149 is not limited to theabove-described embodiment. For example, the length of the plate-shapedportion 149 a in the Y-axis direction may be equal to or smaller thanthe length of the torsion bars 147 and 148. The width of theplate-shaped portion 149 a (the length in the X-axis direction) may beequal to or smaller than the width of the torsion bars 147 and 148. Theplate-shaped portion 149 a may extend in an arbitrary direction. Thenon-linear relaxation spring 149 may include single or three or moreplate-shaped portions 149 a. In the above-described embodiment, the pairof non-linear relaxation springs 149 are provided in the first elasticsupport portion 14, but single or three or more non-linear relaxationsprings 149 may be provided. The non-linear relaxation spring 149 maynot include the plate-shaped portion 149 a. The same applies to thenon-linear relaxation spring 159.

As in the optical module 1, the fixed mirror 21 may be disposed not onlyat a position right below the first optical function portion 17 but alsoat a position right below the second optical function portion 18. Withthis configuration, it is possible to suppress deterioration in themovable performance of the movable mirror 11 and an increase in the sizeof the entire device while realizing multi-functionality of the deviceby using the second optical function portion 18 in the same manner asthe first optical function portion 17. The fixed mirror 21 may beprovided on the main surface 12 a of the device layer 52. In this case,the light passage opening portion functioning as the first opticalfunction portion 17 and the second optical function portion 18 is notformed in the SOI substrate 50. The optical module 1 is not limited toone constituting the FTIR, but may constitute another optical system.

Further, in the above-described embodiment, the first comb finger 161 aand the second comb finger 162 a which are adjacent to each other mayface each other in the direction in which the movable mirror 11 hashigher or highest external force resistance. That is, a side surface ofthe first comb finger 161 a and a side surface of the second comb finger162 a facing each other may face each other in the direction in whichthe movable mirror 11 has higher or highest external force resistance.As an example, at least one of the first comb finger 161 a and thesecond comb finger 162 a may extend while being inclined with respect toa plane perpendicular to a direction in which the movable mirror 11 hashigher or highest external force resistance. Alternatively, at least oneof the first comb finger 161 a and the second comb finger 162 a may bebent in an arcuate shape when viewed from the Z-axis direction. The sameapplies to the first comb finger 163 a and the second comb finger 164 a.

Each configuration in one embodiment or modified example described abovecan be arbitrarily applied to each configuration in another embodimentor modified example.

REFERENCE SIGNS LIST

10: optical device, 11: movable mirror (movable portion), 11 a: mirrorsurface (optical function portion), 12: base, 14: first elastic supportportion (elastic support portion), 15: second elastic support portion(elastic support portion), 141, 151: lever, 144, 154: electrode supportmember, 147, 157: first torsion bar (torsion bar), 161, 163: first combelectrode, 161 a, 163 a: first comb finger, 162, 164: second combelectrode, 162 a, 164 a: second comb finger.

1: An optical device comprising: a base; a movable portion whichincludes an optical function portion; an elastic support portion whichis connected between the base and the movable portion and supports themovable portion so that the movable portion is movable along a firstdirection; a first comb electrode which is provided to the base andincludes a plurality of first comb fingers; and a second comb electrodewhich is provided to at least one of the movable portion and the elasticsupport portion and includes a plurality of second comb fingers arrangedalternately with the plurality of first comb fingers, wherein theelastic support portion includes a torsion bar extending along a seconddirection perpendicular to the first direction and a lever connected tothe torsion bar, wherein the second comb electrode is provided to aportion of at least one of the movable portion and the elastic supportportion, the portion being located on the optical function portion sidewith respect to the torsion bar, and wherein the first comb finger andthe second comb finger which are adjacent to each other face each otherin a direction in which the movable portion has higher external forceresistance, of the second direction and a third direction perpendicularto the first direction and the second direction. 2: The optical deviceaccording to claim 1, wherein a pair of the elastic support portions aredisposed on both sides of the movable portion in the third direction. 3:The optical device according to claim 1, wherein the direction in whichthe movable portion has higher external force resistance is the seconddirection, wherein the elastic support portion further includes anelectrode support member provided on the optical function portion sidewith respect to the torsion bar so as to extend along a planeperpendicular to the first direction, and wherein the second combelectrode is provided along the electrode support member. 4: The opticaldevice according to claim 1, wherein the direction in which the movableportion has higher external force resistance is the third direction, andwherein the second comb electrode is provided along an outer edge of themovable portion. 5: An optical device comprising: a base; a movableportion which includes an optical function portion; an elastic supportportion which is connected between the base and the movable portion andsupports the movable portion so that the movable portion is movablealong a first direction; a first comb electrode which is provided to thebase and includes a plurality of first comb fingers; and a second combelectrode which is provided to at least one of the movable portion andthe elastic support portion and includes a plurality of second combfingers arranged alternately with the plurality of first comb fingers,wherein the elastic support portion includes a torsion bar extendingalong a second direction perpendicular to the first direction and alever connected to the torsion bar, wherein the second comb electrode isprovided to a portion of at least one of the movable portion and theelastic support portion, the portion being located on the opticalfunction portion side with respect to the torsion bar, and wherein thefirst comb finger and the second comb finger which are adjacent to eachother face each other in a direction in which the movable portion hasthe highest external force resistance, of directions perpendicular tothe first direction. 6: An optical device manufacturing methodcomprising: a step of creating a model corresponding to the opticaldevice according to claim 1 and measuring a direction in which themovable portion has higher external force resistance, of the seconddirection and the third direction in the model; and a step ofmanufacturing the optical device so as to correspond to the model whenthe first comb finger and the second comb finger which are adjacent toeach other face each other in the direction in which the movable portionhas higher external force resistance in the model as a result ofmeasuring the direction in which the movable portion has higher externalforce resistance. 7: An optical device manufacturing method comprising:a step of creating a model corresponding to the optical device accordingto claim 5 and measuring a direction in which the movable portion hasthe highest external force resistance, of directions perpendicular tothe first direction in the model; and a step of manufacturing theoptical device so as to correspond to the model when the first combfinger and the second comb finger which are adjacent to each other faceeach other in the direction in which the movable portion has the highestexternal force resistance in the model as a result of measuring thedirection in which the movable portion has the highest external forceresistance.